1. Field of the Invention
The present invention relates to a spindle head unit incorporating a spindle drive motor assembly, more particularly, to such a spindle head unit provided with a built-in heat insulation system between the spindle drive motor and the the spindle as well as the spindle support bearings.
2. Description of the Prior Art
Spindle head units incorporating drive motors, particularly, AC motors, for driving the spindles have come into wide use since they do not require rotation transmitting mechanisms and other auxiliary mechanisms between the spindles of the machine tools and the drive motors. The cutting tools or workpiece holders are attached to the noses of spindles. Such motor-incorporated spindle head units, however, suffer from inevitable generation of heat from the incorporated spindle motors due to the known copper and iron losses. The amount of heat generated increases with the power of the spindle motors and heats the spindle motors by an undesirably high extent, such as several dozen degrees centigrade. Heat transferred from the spindle drive motors to the spindles and to the bearings causes thermal deformation or expansion to the spindles and the bearings, resulting in inaccurate alignment of the spindles. Accordingly, the transfer of such heat has to be suppressed as much as possible.
To reduce this undesirable heat transfer to the spindles and spindle bearings, diverse cooling systems have been devised in conventional spindle head units so as to remove the heat from the spindle drive motors. For example, copending Japanese Patent Application Nos. 57-001006 and 57-001007 of the same applicant as the present application disclose improved cooling systems built in the spindle head units for effectively removing heat from the surfaces of the spindle drive motors. However, no method or arrangement has been adopted for providing effective heat insulation between spindle motors and the spindles and bearings.